Time control system



Patented Nov. 23, 1937 PATENT OFFICE am.zu

um: CON'1'BOL sysmu John l. Kriechbaum. Minneapolls, Mlnn., assimor to MinneapolIs-Bonemll Bemhtor Company, Mhmeapolls, MInn.

wate

Dell

a oorporatlon o! Appllcation November m, 19:4. 8er lal N0. 753,314

21 Clalms.

'Ih1s inventlon relates to I:lme control systems, and ls partlculax:ly dlrected to a. tlmlng system whlch closes a. clrcult a predetermlned Iength 015 tlme after the closlng 01' another circult.

Although the t1ming system 01' th1s inventlon Is o! genera1 ut1llty anal may be used wherever such a t1ming sequence is desired, II; flnds particular utillty in the control 01 ga.s flred ovens to Insure the operation 013 the exhaust fan thereof for a predetermined length cf t1me betore the gas Is turned on in order to 11d the oven 015 hlghly combustlble and explosive gases.

II: is an object of this invention to provide a time control system 1'-or closlng a circuit a predetermined len.th of tlme alter the closing o1 anther clrcuit. A

lt is another object cf th1s invention to provlde a, timecontrol system 101 closlng a, circult a predetermined length of time after the closlng of another circu1t in which power fallure protection Is s.florded in that lt the power falls at any time durlng the tlming 'cycle a complete recycle must be made be1'ore the second clrcult o1 externe] load circult can be cl0sed.

A further object Is to provlde a time control system for a. gas fired oven in which an e1:hau.st fan ls operated a. predetermlned length of time before the gas is turned on in order to rld the oven of highly combustible und explosive gases. A still Iurther object 1s 130 provide a tlme coutrol system tor s. gas flred oven of the type spaifled whlch provldes tot power failure protectlon so that the gas valve cann0t be turned 0n until s.fter the exhaust tan has operated tor at least a predetermined length 01 time.

Other objects and advantages will becoxne apparent I;o those skilled in the art by reterrlng I0 the accompanying speciflcation und drawing, in which:

Fig. 1 is a. dlagrammatic view 01' one !orm o! my Invention, und

Flg. 2 is a dlagrammatic vlew o1 another l'orm 01 my Inventlon, both of sa1d flgures showlng the parts in the ofl! positlon.

Although the system is considered to be 013 Seneral utlllty, it is shown as applied to a, control for a gas flred oven wh1reinit is contemplated to operate an exhaust fs.n for a predetermlned length ot time before the gas is' turned on. In gas fired ovens, especlally in the type used for enamelling and the like highly combustlble und explosive gases are glven ot! by-the procesSes accomplished thereln; theretore, lt is necessary to rld the furnace of all these hlghly combustible and explosive gases before the furnace 1s heated.

Consequently, provision is hereby made for operatlng the exhsust (an a prede.termined length o! time before the 888 is turned 011 to heat the gas flred oven.

Referring now to Flg. 1, the exhaust fan is diagrammatically shown und designated at; I0 und 1s operated by an electrlc motor II, and the gas valve is diagrammatically shown and designated at I2, und lt is operated by a, solenoid I3. These structures are old in the art, und a more speciflc description thereof ls not ponsldered necessary.

I4 and I5 desiznate line wires leading trom some power source (not shown), and they a.re connectedat times by means o1! a d0ub1e-poled slngle-throw switch IG .to w1res I'I and I8 which lead to the fa.n motor II. When the switch I6 1s closed. current flows through wires I'I and I8 from the llne wires II und I5 to operate the motor II to drlve the exhaust Ian I0.

A switch in the form 01 a push button 20 1s connected by means of a. wire I9 I;o the wire I'I and by a wire2l to a coil 22 form1ng the fleld o1 an electrlc tlmlng motor having a rotor 23. The other end 01 the fleld 22 01 the electrlc thn Ing motor is connected to -the wlre I3 by means 012 a wire 24. When the push button sw1bch 20 is closed by pressing thereon, a circu1t 1s completed from wlre I'I through w1re I9, switch 20, wlre 2I, coil 22, and wlre 23 I;o w1re I8 to energize the timlng motor to rota.te the rotor 23. When the swltch 23 1s opened by relleving the pressure thereon, fleld cofl 22 01 the motor 1s not energlzed by the above circuit. 'I'he above circult when closed completes a starting circuit for the motor.

'1he motor rotor 23 has a motor plnlon 23. which drives a reductlon gear tra.ln generally designated a.t 23 to rotate ca.ms 2'l, 23. and 23. 'I'he reducflon gearing 26 lnay be o! any deslred type and may reduce the speed of the cams 21, 28, und 23 with respect to the motor roter 23 as deslred, determined upon I :he amount of rotation of the cams requlrd in a given interval o1 tlme. Cum 21 has a low dwell 30 thereon of compan- I:1Vely short length, wh1le cam 23 has a. h1gh dwell 3I thereon, also 01 comparatively short length. The cam designaced generally at 23 Is made up of two cooperating cam d1scs 32 and 33, the cum disc 32 being flxed for rotation, am! the cam disc 33 being adjustable relative 1:0 the cam dlsc 32 by.means of a slot 34 located in the cam d1sc 33 and a pin 35 secured to the cam dlsc 32 operatlng in said slot. Suitable means are provided on the pin 35 to maintain the cam dlscs 32 und 33 5 in their relative adju'sted posltlons. It will be dwells of the ca.m discs 32 and 33 are adjacenl:

each other, the eflectlve surface cf the cam 29 is substantially 180. Thls efiective surface is increased by rotating the cam disc 33 with re;pect to the cam disc 32, aud the amount of such rotation determines the efiective length of the dwell of the cam 29. By this means the efiective dwell of cam 29 may vary in amount from substantially 180 t0 almost 360.

Thecams 21, 28, and 29 are fiied in e, definite relation with respect to each other. By rotating the cams '21, 2B, and 25 in a counter-clockwise direction as shown by the arrows, low dgwell 30 of cam 21 becomes effective first, then the high w ll of the cam disc 32 becomes efiective, and then the high dwell 31 of the cam28 becom'es efiective in that definite sequence.

Cooperating with ehe cam 21 1s a cam follower 36 having a contact 31 thereon which engages a stationary contact 55 when the follower 55 1s out 016 engagement with the low dwell 55 cf the cam 21. Cooperating w1th the cam 25 is a cam follower 39 having a contact 55 thereon which engages the stationary contact M when the high dwell 31 of the cam 28 engages its follower 35. Cooperating with the cam 25 15 a cam follower 52 having a contact 53 thereon which engages the stationary contact M when' the cam follower 52 is out of engagement with the high dwell of the cam 25.

Assuming that the parts are in the positions shown in Fig. 1, the motor 1s energized to rotate the cams 21, 28, and 25 in a counter-clockwise direction. The firsc sequence of operation caused thereby is the closing of the contacts 31 and 38'; the second sequence is the opening of the contacts 53 and M; and the third sequence 15 the closing of the contacts 65 and 65. 15 will Yoe noted from this construction that contacts 51 and.

38 are open only momentarily, tha.t cont'acts 53 and M are open for a. comparatively long tlme, anal that contacts 45 and M are closed only momentarily.

Wire 21 is connected by means of a, wire 55 with the movable contact 31, and the stationary comtact 35 is connected by means of a wire 51 to a wire 52 which ls connected to one side of a cut-out switch 53. The other side cf the cut-out swltch 53 is connected by means of a wire 55 with the Wire 11. The swltc'h 53 1s normally closed, but upon opening it afiords a means for sh utting down the timing system in a manner which will -be pointed out more clearly hereafter. 'I'he switch 53 may also take the form of a simple push button switch since lt is necessary only to bre9,k the cixcuitcontrolled thereby momen- A tarily to ca.use a shu t down. Ihis wiring completes a holding circuit from the wlre I1 through the wire 54, switch 53, wire52, wire 5fl, contact' 36, contact 31, wlre 50, wire 2 icoi1 22, and wire 24 to wire I8. By reason of th1s circuit, the field 0011 22 of the motor is maintained energized when the contacts 31 a.nd 38 are in engagement even though the push button switch 25 is open. A coil 55 of a. relay is connected 1:0 the field coil 22 of th'e motor by means of a wire 55. "I'he other end of the relay coil 56 is connected bymeans of a wire 51 t0 a wlre 58 which ls counected to the movable contact 55 of the cam follower 33, and the cooperatlng stationa.ry contact 4l 1s connected by a wire 59 to the w1re 5I. When the-high dwell 3I of the cam 28 engages the cum follower 39 to cause ebntacts 40 and ll engag6, a timing starting circult is completed from the wir'e 11 through w1re 54, cut-out switch 53, wlre 52, wire 51, wire 59, stationary contact GI, movable oontact M1, wire 58, wlre 51, relay co1l 55, wire 55, anti w1re 24 1:0 wlre I8.

55 and 65 designate switch arms which are normally maintained in the' right posltlon by means of springs or gravity or other means (not shown), and they are operathzely connected together and to the relay coil 56 by means of a roii 52.. Switch arms 55 and 51 are moved to the left upon energization of the coil 55 to engage contacts 53 and. 5 3, respectively. When the coil 55 is deenqrgized, the switches 519 and 58 am moved out of engagement with the contat:ts 53 and 55, respectively. Switch arm 55 is connected by means 02 a wire 55 with the wire 59.

When the rela.y co1l 55 is enargized to move switclp. arm 50 into enagement with.switch arm 53 upon closing of the timing starting circuit autlined above, a timing holding circuiis completed by thismovement from wire I1 through w1re 55, cut-out sw1tch 52-3, wire 52, wire 51, wire 55, wre 55, switch arm 55, contact 53, wire 51, relax; co1ll 55, wire 55, and wire 25 to wire '15. From thls 1i: is Seen that the relay coil 563 is maintained energlzed by the timing holding circuit regardless 01 whetheror, not the contacts 55 anti %fl are in er out of engagemnt.

The movable contact 653 is connected. to tlne wire 52 oy means of a wire 55, anti the stationary contact 55 is connected by a, wre? 51 with-the contact E 3, The switch arm 51 is connected by mea.ns o:f a wire 53 to the solenold 333, and the solenoid 85 is connectd. by another w1re 55 i;o the wire E8. When the switch arm 58 is movezi into engagement with the contact 55 by the relay ooil 55 in the manner pointed out above, and when the 'contact 53 engagesthestationary comtact 5 3 by reason of the cam follower 52 moving off cf the high dw'ell of the cam 25, a va1ve opera.ting clrcuit is completed from wire 11 through wire 55, cut-out switch 55, wire 52, wre E5, movable contact' 55, stationary contact 55, wire 51, contact 55, switch arm 59, wire 55, solenold 95, and wlre 55 1:0 wire 18. When this valve opera.tlng circuit is completed in the manner pointed out immecliately above, solenoid 55 is energlzed. i:o open valve I2 parmit flow of gas from some source (not shown) into the gas fired oven (not shown). Thls va1ve op8rating circuit is broken either by disengagement of contacts 53 and 415 or by dis6ngagement of switch arm from cant8&t 56.

The operation cf the device is as follows: Assuming that the parts are in the normal of1' position, as shown in Fig. 1, switch 15 is closedto energize the motor i i to operate the exhaust fa.n W. When push button switch 20 is closed by manually pressing thereon, the timing 'motor starting circuit is completed therethrough to energize the field coi1 22 rotate the rotor 23 of the timing mdtor. Rotation of this motor causes counter-clockwise rota:tion of the cams 21, 28, and 29 in the direction shown by the arrows through the reduction gearing 26. The flrst mcremsnt of movement of cams 21, 28, and 29 causes follower 36 by reason of 1ts rlding out of t.he low dwell 30 of cam 21 to close contacts 31 and 38, thereby causing the timing motor holding clrcuit to continue (ene1gization of the field coll 22 of the timing moto;r to continue opetation o1 the roter 23, and consequently the cams 21, 28, and 29. After contacts 31 a.nd 38 are brouht into engagement by the cum 21,.push button swltch 20 muy be releused, und the tlming motor will still be operuted by this timlng motor holdlng clrcult.

A further increment of mqvementcauses the hlgh dwell cf cum disc 32 to enguge the cum follower 42 to separate the contucts 43 und 44. A still further lncrement .of movement cuuses the high dwell 3I cf cum 28 to enguge cum 1ollower 38 to close contucts 40 und 4I, thereby complet- Ing the tlmlng sturting clrcuit us outllned. ubove. Upon completlcn of this tlmlng starting clrcuit, coil 58 ls energlzed to draw switches 60 und 6I into engugement wlth contucts 63 und, respectively. When swltch 60 enguges contuct 63, u timlng holdlng circult ls completed us outllned above to mulntuin the coil 56 energlzed. Slnce the coil 56 ls energized by this tlming holdlng circult, the sepurution 01 the contucts 40 und 41 by reuson cf the hlgh dwell 3I of the cum 28 dlsenguglng the cum follower 33 will not utfect the reluy coil 56. Slnce c ontucts 43 und 44 were sepuruted by the above -mentioned second Increment cf movement, a, clrcult ls not completed by the engaementcf switch arm 6I with contuct 64 to open the vulve I2. Upon Iurther rotutlon 02 the tlmlng motor, und consequently the cums 21, 28, und 29, contucts 43 und 44 will be held sepuruted until the cum follower 42 rldes oft of the hlgh dwell of the cum disc 33, whereby comtacts 43 und 44 enguge to complete the vulve opment umounts to substuntiully 360, cum l'ollower 36 rides into the low dwell 30 cf the cum 21 to separate contucts 31und 38 to open the tlmlng motor holdlng 8::ircult to deenergize the field coil 22 cf thetlmlng motor to stop rotution of the rotor 23, und consequently the cams 21, 28, und 29. Slnce ut this point the reluy coil 56 ls energlzed by reuson of the timing holding circult to maintuin the swltch arm 6I in engugement wit-h the contuct 64, und since the contucts 43 und 44 ure still In engugement, the vulve operuting clrcuit is still closed, und gus is still being sent through the va.lve I2 into the gus fired oven.

In order to shut off the flow of gus through the gus vulve I2 und still muintuin the fun I in operutlon, swltch 53 ls opened to breuk the timlng holdlhg circult und the valve operuting circuit to deenerglze the solenold I3 to permit closlng of the valve I2. If lt be desired tostop the operatlon cf the fun I0 und close the vulve I2, er, In other words, effect u complete shut-down of the devlce, switch I6 ls opened.

Since the reluy coil 56 is energized during the tlming cycle und also during the perlod ufter the timlng cycle hus bee1 1 completed, u power fuilure in the llnes I4 und I5 will be directly reflected by deenergizution cf the reluy coil 56. When the coil 56 is so deenerglzed, swltch urms 60 und 6I ure moved out cf engugement wlth contacts 63 und. 64 to open the timlng holding circuit und the va.lve operuting circuit, thereby deenergizing the solenold I3 und permittlng closing cf the vulve I2 to shut olf the gus supply to the gus fired oven. Slnce upon power fullure the. switch urms 60 und 6I ure moved out cf engugement with the contucts 63 und 64 by'deenergizutlon of the coil 56, coil 56 muy not be reenergized upon resumption of power until the high dwell'3l 0f the cum 28 enguges the cum follower 39 to close contucts 40 und 4I to complete the timing sturting circuit outlined ubove. By reuson of this, lt is nacessary to operute the tlming mechunlsm through -u new und. complete tlmlng cycle in the munner pointed out abcve.

By this construction a vulve operuting circult ls, closed a. predetermlned tlme ufter the closing of the motor sturting circuit, und in no wuy ls lt possible to close this vulve operutlng circult until thislntervul of tilne hus elupsed. Even if power failure occurs durlng this timing cycle, by the construction shown und described this predetermined time cycle cannot be decreased upon resumption of power in the lines I4 und I5.

Referring 'now to Fig. 2 wherein is shown unother form cf my invention, it is contempluted to use the sume exhuust fun I0 drlven by the electrlc motor II und the sume gus vulve I2 0peruted by the solenold I3. A similur tlming motor ls used huvlng the motor field 001122 und u roter 23 which d.rlves u motor pinion 25 which drives through u sultuble geur reduction 26 cams 21, 28, und 29. In this mcdificution, us in the prevlous modificutlon, cum 21 hus a. low dwell 30 cf relutlvely short durutlon cum 28 hus u lngh dwell 3I of relutively short duration, und cum 29 comprised cf cum discs 32 und 33 mudc adjustuble by meuns of the slot 34 und pin 35 hus u variable high dwell udjpstuble from substantia.lly 180 to about 360.

Here aguin, the low dwell 30 of cum 21 coucts with u cum follower 36 to muke und breuk c0ntucts 31 und 38, und the high dwell 3I of the cum 28 coacts with the cum follower 39 to muke und break contucts 40 und 4I. The hlgh dwell of the cum discs32 und 33 cf the cum 29 couct with the cum follower 42 to muke und breuk the contucts 43 und 44 as ubove. 'I'his modification also comtemplutes the use of the same relay huving the sume coil 56.

This modificutlon, however, o-mits the push button switch 20 und the out-out switch 53.

desigriutes a. switch arm movuble ulternutely into engugement wlth contucts 1I und 12. 13 designutes a. switch arm which moves into engugement wlth u contuct 14. The switch urms 10 und 13 are ccnnected together by means cf u rod for synchronous movement, und this rod 15 ls operutecl by the reluy coil 56 t0 move the switch urms 10 und 13 from one position to the other. Upon energizution o1 the coil 56, switch arm 10 ls moved out of engugement with coutuct 12 und into engugement wlth contuct II und switch arm 13 is movecl into engugement Wlth contuct 14 by the rod 15. Upon deenergizution of the reluy coil 56, the switch arm 13 is moved out of engugement with the contuct 14, und the swit'ch arm 10 is moved out of engugement with the contuct 1I und into engugement with the contuct 12 by meuns cf springs, gruvlty, or some 0ther meuns (not shown).

16 und 11 designute line wires leuding from some source (not shown) which ure enguged by meuns o1 u bi-pole slngle-thrcw switch 18 to transmit energy into the wires 19 und 00 which leud to the exhuust fun motor II. When the switch 18 ls closed the motor II is energized to operute the exhulist fun I0. The wire 19 is comnected by meuns of u wire 8I, u wire 82, a. wlre 83,

und a wire 88 I2o the switch arm 'IB. The coutacI; I2 12 conmcted by means o! a wire 35 a.nc'l a wire 83 tc one end 01 the fleld coil 22 of the timing mobor, end the other end o! the fleld coll 22 I.s connected by a wire 31 a.nd awlre 03 to the wire 83.

These eonnections complete a. tim1ng motor starbing circult from '!9 through wire 3I, wire 3-2, wire 83, wire" ;swltch arm I0, contact I2, wlr 80, wire 35, flehfi:oil 22, wire 87, and wire 53 00 wire to energize the fleld coi1 22 cf the tlming motor to rotate the rotor 23 upon closlxlg 01 the swiltch I3. Rotor 23 drivesthe cams 2I, 23, und 23 through the gea.r reduction 23 in exactly the sa.me manner as in"-the modlflcation polnted ouI: above.

Wlre 321s connected 120 contact 38 by means 01 wire 33 to complete a. tlming motor holding circult 1mm wire I9 through wire 3I, wire 82, wire 00, contact 33, contact 3'I wire 83, field coil 22, wire 3'I, and wire 88 to ins of oontacts 31 and 38 y he riding out of the cum follower 30 from th 1ow dwell 30 cf the ca.m 2'I.

Movable contact 40 is connected by means of a wire and a. wire 3I 170 one end of the relay coil 56, and the other end 01 the relay coil 55 is connected by a. wire 92 to the wire 88. These canr.iectlons complete a. tiznlng starting circuit upon engagement cf contacts 40 a.nd 4I causedby the high dwell 3I of the cam 20 engaging thg cum follower 30, from wire 'I3through wire 8I wire 82, wire 83, stationary contact 4I, movable c on- Isact I0, wire 50, wire 9I, relay coil 55, wire 92, and wire 88 to wire 80. When the relay coil 56 Is so energized it moves swltch arm I0 'out 02 engagement with centact I2 a.nd into engagement with contact II and moves switch arm 13 into engagement with coutact II. By reason of switch arm I0 engaglng contact II in the manner just described, a I;iming holding clrcult is completed from wire I9 through wire 8I, wire 32, wire 83, wire 84, switch arm III, contact II, wire 3I, relay coil 56, wire 92. and wire 38 to wire 00 to maintain the relay coil 56 energlzed whether or not contacts 40 and 4I are disensa3'ed.

Wire 8I ls connected by means cf a wire 93 wlth the mova.ble contact 43, a.nd the statlonary contact M is connected by means of a. wire 94 with the contact IG. The switch arm 13 is connected by means of a wire to the solenoid I3, am]. the solenoid I3 is connected by awire 35 to the wire 80.

When switch arm 13 engages contact I4 and when contact 43 engages contact H by reason of the cum follower 42 sliding ofi cf the high dwell of the ca.m discs 32 and 33 of the cum 29, a valve operating eircultis completed from wire 19 through wire 8I, wire 93, movable contact 43, stationary contact H, wire 9l contact I4, switch arm I3, wire 95, solenoid I3, and wire 96 to wire 80 to energize the solenoid I3 to open the va.lve I2 I:o allow gas flow 1mm some source (not shown) into the gas fired oven (not shown) Since the cams 2'I, 28, and 23 are the same as erate the exha.ust tan I0, und the starting cira:u.it described above is completed to energlze the fleld coil 22 to rotate i;he rotor 22 of'the tim1ng motor, and consequently to rotate the caxns 21, 28, a.nd 29. Upon the firsl: increment o! move ment, contacts 37 and. 38 are closed to complete' the mo!;or holding circuit. above despribed 00 maintaln the field co1l 22 of the timing mntor enexglzed.

Upon turther movement 01 the cams 2I, 20, and 29 contacts 03 and IM are separated by the cam. 29, and upon a still further movement cams 40 and GI are brought lni;o engagement by the cam 20 to complete a timlng starting circuit above desc1ribed to energize Ishe coi1 55 00 move I;he

swltch arm I0 out of engagement with the coutact 'I2and into engagement with the conta.ct II and 'Iso move the switch arm 13 into engagement with the contact IQ. Movement of the switch arm 10 into engagement with the contact II completes the timing holding circuit outlined above to maintain the coil 53 energized, but the movement of I;he switch arm 13 into enagement with the contact I4 has no efiect because aI? this time I:he contacts 43 and M are separated -by the cam 29, y

Upon a iurther relatively large moven1ent as debermined by the length of the high dwel1 01 the cam 29, contact 33 engages contact 44 to complete the valve operating circuit above descrlbed to energize the sqlenoid I3 to open the vaive I2 to permlt the flow of gas into the gas fired oven.

'Upon a further movement of the .cams I;o the engagement, the solenoid I3 will still be energized to maintain the valve I2 open.

Upon power failure, relay coi1 56 will become deenergized to permit movement of switch arms 70 and I3 out of engagement with contacts II and M, respectively, and to move switcli arm I0 into engagement with contact I2. By such movement ca.used by power failure as reflected in the deenergization of the relay c.0il 56, the timing holding circuit and the valve operating circuit are opened so that upon resumption of power in the lines I6 and,'l'l the solenoid I3 may not be energized to openthe valve I2; therefore, a com-* plete recycle which necessa.rily requires a. complete time interval to elapse between the starting of the fa.n I0 and the opening of I1he valve I2 must be'had.

From I;he above it is seen that I have invented a. tlx ne contro1 mechanism for closing a; circuit a predetermined length of time a.fter the closing cf another circuit in which power failure protection is afiorded in that if the power fails a1; any time during the timing cycle a complete recycle must be made before I;he second circuit er external load circult can be' closed. II: will also be seen that I have invented a control system for a. gas flred oven which requires the xhaust fan thereof to be operated for a predetermined Iength of tlme before gas may be supplied to the oven anti in which by no manner whatsoever may gas be supplied to the gas fired oven before this predetermined time has elapsed even though power failure and other conditions may come into play tend decrease this time interval.

While several embodiments cf this invention have been shown und descrlbed, it is obvlous that many modiflca.tlons ma.y be apparent to those skflled in the art; for example, the push bntton' swltch und the cut-cn'xl: swltch may be elimlnated 5 froxn the form shown in Flg. 1 and may be properly lnserted in the form shown in F'ig. 2 without alterlng the scope o1 this inventlon. Consequently. th1s inventlon ls to be llmlted only by the sooj:e 01 the appended clalmg und theprior 10 art.

I clalm as my lnvention:

1.In a. system o1 the character described, a. device to 'be operated following the lapse ot a substantial tlme lnterval, tlmlng mea.ns, mecha- 15 nlsm placed in opemflnn by the timing means to Start a tlmlng cycle, andmeans controlled by the tlm1ng mea.ns and the mechanism for placing the device in opera.tlon a substantial t1me alter the starting cf the tlmlng cycle.

20 2. In a system of the charatet described a devlce to be operated following the la.pse of a substantial time interva.l, timing means, mechan1sm placed in operation by the timlng means to starta tlming cycle, means controlled by the 26 tim*ng means and the mechanlsm for placing the device i"n operation a. substantial time after the starting of the Timing cycle andthereby terminv.tlng the timing cycle, and means for prevent- Ing operation of the device in case sa.ld mecha- 30 nism becomes inoperative during the timjng cycle whereby the la.pse 015 a complete timing cycle is required to plane the device in operation.

3. In a system o1. the characte; described, a. device to be operated following the lapse of a #6 substantla.l time interval, timing mea.ns mecha nism placed in operation by the timing means to start a. tlmlng cycle, means' for mainta.lning the mechanism in operation durlng the'tlming cycle, and means controlled by the timing means 40 und the mechanisln for placing the device in operation a substantial time alter the starting 01 the timing cycle.

4. In a system o1 the character descrlbed, a devlce to be' operated Iollowing the lapse cf a 45 substantial time interva.l, timing means, mechanism placed in operation by the timing means to start a timlng cycle, means for maintaining the mech'anism in operation during the timing cycle, means controlled by the timing means and I the mechanism for placing the device in operatlon a substantial time after the starting of the timlng cycle und thereby terminating the timing cycle, und means for preventing operation of the device in case said mechanism becomes inopera- 56 tlve durlng the tix ning cycle whereby the la.pse

o1. a. complete timing cycle ls required to pla.ce the device in operation.

5. In a system of the character described, a

device to be placed in operation following the 60 lapse of a. substantial time interval, tlming means,

means for p1-acing the tlming mea.ns in operation, means controlled by the timing means-for continuing the timing means in operatlon, mechanism placed in operatinn by the t-iming mea.ns

l to start a, timing cycle, means controlled by the tlming means a.nd the mechanism for placlng the device in operbtion a, substantial tlme afte;

the starting 01 the timing cycle and thereby termlnatlng the timing cycle, a.nd means for pre- 70 venting operation o! the device in case seid mechanism becomes imperative during the timing cyc1e whereby the lapse ot a. complete timing cycle is re'quired to place the device in operation.

6. In a system of the character described, a.

78 dbvice to be placed in operation following the lapse of a substantial time interval, timing means, means for placing the 'timing means in operation, 1r'1eans controlled by the tlming means for contlnuing the timing means in operatlon mechanism placed in operation by the tir'nlng mans to sta.rt a. timing cycle, means for maintainlng the mechanism In operation durlng the tlmlng cycle, und means controlled by the tlming means lind the mechanism for placlng the dev1ce in Operation a. substantial tlme alter the starting 10 of the timlng cycle.

7. In a system for placing a.first devic in op ration and then a second device in operatlon following the la.pse ofa. substantial time interval the combination 01 ming mea.ns, means for -placing the flrst device und the timing means in operatlon, mechanism placed in operation by the timing means to sta.rt a timing cycle, und means controlled by the tdming means and the mechanlsm for placing the second device in operatlon a. s1;bstantial time after the starting of the timing cyc e.

8. In a system for placing a first device in Operation and then a second device in operatlon following the lapse o1 a. substantlal time interva;l. the combina.tion of timi'ng means, means for placing the fl rst device and the timing means in operation, mechanism placed in operation by the timing means to start a. t.iming cycle, means coutrolled by the timing mea.ns and the mechanlsm for pla.cing the second device In operatlon a. substantial t1me after the staxting of the tlming cycle and thereby terminatdng the timlng cycle, a.nd means for preventlng operation 01 the second device in case said mechanism becomes lnoperative durinq the timing cycle whereby the lapse of a complete timing cycle is required to plane the second device in operation.

9. In a. system for placirig a flrst device in operation und then a second device in operation following the lapse of a substantial tlme lnterval, the combination of timing means, means for .placing the flrst device and the timing means in operatlon, mechanism placed in operation by the timing means to sta.rt a timing cycle, means for maintaining the mechanism in operation durlng the tlming cycle, and means controlled by the -timing means and the mechanismfor placing the second device in operation a substantial tlme after the starting of the timing cycle.

10. In a system for placing a flrst device in operatlonand then a second device in operation following the lapse 01 1;. substantlal time interval, the combination of timing means, means for pla.cing the flrst device and the timing means in operatlon, mechanism placed in operatlon bv the timing means to starb a tixning cycle, means for maintaining the mechanism in operatlon du'ring the timing cycle, means controlled by the timing means and the mechanism feiplacing the second device in operation a substantial time after the starting of the timing cycle thereby term na.ting the timing cycle, and means for preventing operation of the second device in case said mechanism becomes imperative during the tim- Ing cycle whereby the lapse of a complete Timing cycle is required to place the second device in operation.

11. In a system of the character described. a. device to be placed in operation following the 121388 of a substantial time interval, timing means,

a coll, a switch operated thereby, a first switch operated by the timing means to complete an energizing cixcuit for the coll for closing its associated swltch to statt a timlng cycle, und a second switch opera.ted by the timing means e substantial tlme after operatlon cf the first switch to complete a, circuit through the sw1tch operated by the coil for plcing the device in operation.

12. In a system for placing a: .first device in operation and then a. second device in operatlon following the lapse of a, substantial filme interval, the combinatlon of timing means, means for plac- Ing the first device and the tlming means in operi':ion, a. cofl, a swltch operated thereby, a. flrst s w1tch operated by the timing means to complete an energizing clrcuit for the coil for closing 1ts associated switch," und a; second switchop8rated by the timing means a substantlal time after operation of the flrst swltch to complete a ircuit through the switch operated by the coil for plac- 111g the second device in operation.

13. In a. timing device of the character described, a, device 1:0 be oper'ated, a. motor, timing means operated by said mobor, means completing a. circuit t0 operate sald motor, a coil, a. pair'of switches operated thereby, means operated by said. timing means momentarily to comp1ete a. first circuit through seid coil 1:0 close seid switches, a second circuit completed through said coil and one of said switches to maintain seid. switches closed after opening 012 seid first circuit through seid coi1, and means operated by seid timing means to close a. circuit through the other of seid swltches to operate said device a predetermined time a.fter the closing o1 said switches.

'14. In a timing device of the character descrlbed, a device to be operated, a. motor, tim- Ing means operated by seid motor, means complet1ng a. clrcuit to operate said motor, a coil, a. palr of switches operated thereby, means operated by seid timing means momentarily to complete a. first circuit through said coil to close seid swltches, a. second circuit completed thrqugh said co1l am]. one of said swltches to maintain said swltches closed after opening of seid first circu1t through said coil, means operated by said timing meansto close a circuit through the other cf seid switches to operate said device a predetermined time after the closlng of seid switches, and mens for opening said switches upon a failure of current fiow through said coil.

15. In a tlming device of the character described, a device to be operated, a motor, timing means operated by said motor, means complet- Ing a circuit to operate said motox, a. co11, a pair o! switches operai:ed thereby, means operated by sald timing 1:neans momentarily to complete a firsi: circuit through saidl coil 1:0 close said switches, a second circuii: completed through said coil and one cf said switches to malntain seid switches closed after opening of seid first circuit through said. coil, and means operated by 'said timing means 1:0 close a circuit through the other of said switches 1:0 operate said device a predetermined time after the closing cf seid switches, and means for opening said switches upon power failu1'e 1:0 prevent operation of seid device anti requiring a, complete recycle upon resumption of power 1:0 operate said device.

16.. In a. tlming device cf the character described a device to be operated, a. motor, timing means operated by said motpr, means completing a circuit to Start said motor, means operated by said timing means to complete a motor holdlng circuit 1:0 maintaln sald motor in operation during said timing cycle, a coil, a. palr of switches operated thereby, means operated by said timing means to complete a. first: clreuit 'through seid 0011 to close said switches, a, second circuit cumpleted through said co ll und one of seid swltches to malntain said switches closed after openlhg of seid firsi: clrcuit through said coi1, a11d means operated by seid timing mea.ns 1:0 close e. clrcuit scribed, a. device to be operated, a motor tlmlng means operated by seid motor, means completing a ci1cuit to start said motor, means operated by said timing mearis to complete a motor holding circuii: to maintain seid motor in operation durlng sa.id timing cycle, a co1l, a pa.lr of swii:ches operated -thereby, means operated by said tlm1ng -means to complete a flrst circuit through sald coil to close said switches, a second circuit' completed through seid 0011 and one of sald switches to gnaintain sa.id switches closed after opening of seid first circuit through said coil, mea.ns operat:ed by sald t iming means to close a circult through the other of said switches to place seid device in operation a. predetermlned time afl:er the closing 0f said switches, and means for opening seid switches upon power failure whereby a c'omplete r'ecycle is required upon resumption of power to pla.ce said device in operat1on.

18. In a gas fired oven, an exhaust fan, a. gas valve, means for operating the exhaust fan, tim- Ing mea'ns, means for placing the timing means in operation, mechanism coni;rolled by the tlm1ng means and the means for oberatingthe exha.ust fan, means co'ntrolled by the timing means und the mechanism for openlng the gas valve a. predetermined time after the timing means is placed in operatlon, said mechanism preventing opening of the gas valve 1f the operating means for the exhaust fan is no1: operative.

19. A control system for a gas fired oven having an exhaust fan und a gas valve, the combination of timing means, means for simu1tan(a0usly placing the exhaust fan and the timing means in operation, mechanism controlled by the tlming means, means controlled by the timing means and the mechanism for opening the gas valve a. pre- 20. In a. timing system of the dass desdribed,

the combination of a va.1ve, a fan, -means for operating the fan-, timing means, means for placing the tlming means in oper ation, mechanism coutrolled by the timlng means and the meanS for operating the fan, and means cont-rolled by the timing means and the mechanism for operating the valve a predetermined time afte'r the tlming means is placed in operation, said mechanlsm preventing operation of the va;lve if the operating means for the fan is not eperative.

21. In an oven having a plural.ity of devices foi' controlling the operation thereof, the combination of timing means means for placing the timlng means and one of the devices in operation, mechanism controlled by the timing mealns, means controlled by the timlng means and -the mechanism for placing the other device in operation a predetermined time after the first device is placed in operation, and means gssociating said 

